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  • Atomic, Molecular and Optical Physics  (4)
  • Nitrogen  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 101 (1999), S. 247-256 
    ISSN: 1432-2234
    Keywords: Key words: Density functional one-centre expansion ; Molecular continuum ; Nitrogen ; Trimethylamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. A large-scale one-centre expansion with a radial B-spline basis set is implemented for bound and continuum states. A Kohn-Sham hamiltonian is employed with Hartree and exchange-correlation potentials calculated from the SCF electron density taken from a previous LCAO calculation. An inverse iteration method is used to obtain the continuum wavefunction, from which the cross section and asymmetry parameter are calculated. The convergence with respect to angular momentum and cut-off radius is analysed for N2. The relevance of multipolar contributions even at large distances is shown and suggestions for further improvements are given. In order to show that the present method is suitable to treat systems of moderate size, the (CH3)3N molecule has also been calculated and the results are compared with experiment.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 527-548 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical investigation on the core and valence photoelectron spectra of unsaturated hydrocarbons of increasing complexity, ethylene, trans-butadiene, and trans-hexatriene, has been performed in order to analyze the role of the most important many-body effects on the spectral features and the evolution of these effects along the series. The capability of various configuration interaction (CI) schemes to interpret both the core and the valence ionization satellite structures has been pointed out. The 3h-2v(π)-1p and 2h-1p CI schemes employed, together with an accurate choice of the basis set and the explicit inclusion of the relaxation, has proven to be very useful tools for this kind of study, being sufficiently accurate to explain the most important correlation features and extendible, at the same time, to longer chain systems. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photoionization cross sections are evaluated at the local density level avoiding any potential shape approximation by employing the Stieltjes imaging (ST) technique in conjunction with large (STO) basis LCAO calculations. The ST technique proves accurate in comparison with full continuum calculation on the noble gases ionization. Several choices for the final-state potentials, including different exchange-correlation potentials, are tested on the noble gases, as well as in H2O and CO. Finally, several molecules are investigated employing the transition-state xα potential and the results compared with available experimental data and previous calculations. The accuracy of the proposed approach appears quit comparable to the ab initio static-exchange level, removing spurious resonances associated to the muffin-tin approximation, and should prove useful in the analysis and interpretation of cross-section data for large systems, where it is shown that basis-set requirements become less stringent. The accuracy obtainable for the cross-section profiles allows close comparison with experimental data, which, although showing good general agreement for the shape of the cross-section profile, indicates the need of a further refinement of the theoretical model. © 1995 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 281-289 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A detailed analysis of the performance of the QDPT CI method, which is based on the application of quasi-degenerate perturbation theory (QDPT) within the configuration interaction (CI) approach, is presented by comparing the QDPT CI results and those obtained from the diagonalization of the perturbative space. Calculations of core and valence excitation and ionization spectra of the CO molecule, which is a strongly correlated system, are carried out using a DZ basis set and the accuracy of the eigenvalues and eigenfunctions is checked through the comparison of excitation and ionization energies and intensities. Excellent agreement is obtained for all values, indicating the computational advantages of QDPT CI which is able to explore wide energy ranges without requiring the diagonalization of large spaces. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 507-514 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Application of a purely algebraic least-squares approach in a spline basis to the determination of continuum orbitals in the single-electron molecular case illustrates the excellent numerical properties of the method. Initial work based on a single-center expansion is extended to an LCAO formulation within a single-particle Hamiltonian and to the full multielectron problem in the one-center scheme. Preliminary results on H2+ and He photoionization are reported. © 1994 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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